Month: May 2017

Background

Please check out my previous post on this topic for more information about the general motivation. One thing I never managed to finish with that design was the case, and I also found the requirement for a 12V power supply to be annoying, and the speed adjustment was too limited at the low (useful) end.

Solution

Instead I created a version with a minimalist 3D printed ‘case’, and used an adjustable boost converter to both allow the speed to be taken lower and for the whole thing to be powered from a USB supply. Behold, the USB(ish) Magnetic Stirrer!

Photos

Assembly

As with my previous stirrer, glue the magnets on to the center of the fan as shown in the picture – use the stir bar to ensure the polarity is correct, the stir bar should stick easily to the magnets once they’re in place.

Simply push the ‘case’ into the mounting holes of the fan over the magnets.

Wiring

The wiring is super simple, but feel free to let me know if you think this justifies a circuit diagram:

USB+ to Vin+

USB- to Vin-

Fan+ to Vout+

Fan- to Vout-

FanPWM to Vout-

Note: before connecting the fan, use a voltmeter to set the output voltage somewhere around 6V.

Once everything’s connected, adjust the output voltage to the lowest speed where the fan will reliably start from cold. This is probably the speed to use (too fast and the stir bar will fly off).

Usage Instructions

Just pop the stir bar in a vessel filled with liquid, place on top of the stirrer and turn on. Adjusting the output voltage will adjust the speed – keep the voltage below 12V or you’ll risk damaging your fan. You won’t get great results at voltages above 8V anyway as the bar will fly off.